A Neumann pressure outlet boundary condition for compressible flows

In silico study of the relationships between flow conditions, arterial surface shear stress, and pressure was investigated in a patient with pulmonary arterial hypertension (PAH), using multi-detector Computed Tomography Angiography (CTA) images and Computational Fluid Dynamics (CFD). The CTA images were converted into 3D models and transferred to CFD software for simulations, allowing for patient-specific comparisons between in silico results with clinical right heart catheterization pressure data. The simulations were performed using two different methods of outlet boundary conditions: zero traction and lumped parameter model (LPM) methods. Outlet pressures were set to a constant value in zero traction method, which can produce flow characteristics solely based on the segmented distal arteries, while the lumped parameter model used a three-element Windkessel lumped model to represent the distal vasculature by accounting for resistance, compliance, and impedance of the vasculature. Considering existing limitations with both approaches, it was found that the lumped parameter Windkessel outlet boundary condition provides a better correlation with the clinical RHC pressure results than the zero traction constant pressure outlet boundary condition.

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A diffuse interface IBM for compressible flows with Neumann boundary condition

International Journal of Modern Physics B ◽

10.1142/s0217979220400706 ◽

2020 ◽

Vol 34 (14n16) ◽

pp. 2040070

Author(s):

You Chen ◽

Chang Shu ◽

Yu Sun ◽

Li Ming Yang ◽

Yan Wang

Keyword(s):

Boundary Condition ◽

Neumann Boundary Condition ◽

Compressible Flows ◽

Neumann Boundary ◽

Diffuse Interface ◽

Immersed Boundary ◽

Test Cases ◽

Present Scheme ◽

New Approach ◽

Naca0012 Airfoil

The recently proposed boundary condition-enforced immersed boundary-gas kinetic flux solver (IB-GKFS) is a new approach for simulation of compressible flows with curved and moving boundaries. In the previous application of IB-GKFS, only the Dirichlet boundary condition is considered, which cannot be applied directly to the Neumann boundary condition. In this paper, an auxiliary layer of Lagrangian points is introduced to tackle Neumann boundary condition. Two test cases, including flow around a circular cylinder and flow around a NACA0012 airfoil, are carried out for validation. The results obtained by the present scheme are compared with the reference data available in the literature. Good agreements are achieved, which indicate that the developed method can effectively simulate the compressible flow with Neumann boundary condition.

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The Characteristics-Based Matching (CBM) Method for Compressible Flow With Moving Boundaries and Interfaces

Journal of Fluids Engineering ◽

10.1115/1.1778713 ◽

2004 ◽

Vol 126 (4) ◽

pp. 586-604 ◽

Cited By ~ 13

Author(s):

R. R. Nourgaliev ◽

T. N. Dinh ◽

T. G. Theofanous

Keyword(s):

Boundary Condition ◽

Boundary Conditions ◽

Level Set ◽

Compressible Flows ◽

Radical Change ◽

Subsequent Paper ◽

Ghost Fluid Method ◽

Material Interface ◽

Interface Position ◽

Level Set Function

Recently, Eulerian methods for capturing interfaces in multi-fluid problems become increasingly popular. While these methods can effectively handle significant deformations of interface, the treatment of the boundary conditions in certain classes of compressible flows are known to produce nonphysical oscillations due to the radical change in equation of state across the material interface. One promising recent development to overcome these problems is the Ghost Fluid Method (GFM). The present study initiates a new methodology for boundary condition capturing in multifluid compressible flows. The method, named Characteristics-Based Matching (CBM), capitalizes on recent developments of the level set method and related techniques, i.e., PDE-based re-initialization and extrapolation, and the Ghost Fluid Method (GFM). Specifically, the CBM utilizes the level set function to capture interface position and a GFM-like strategy to tag computational nodes. In difference to the GFM method, which employs a boundary condition capturing in primitive variables, the CBM method implements boundary conditions based on a characteristic decomposition in the direction normal to the boundary. In this way overspecification of boundary conditions is avoided and we believe so will be spurious oscillations. In this paper, we treat (moving or stationary) fluid-solid interfaces and present numerical results for a select set of test cases. Extension to fluid-fluid interfaces will be presented in a subsequent paper.

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VALIDATION OF LOSS-COEFFICIENT-BASED OUTLET BOUNDARY CONDITIONS FOR SIMULATING AORTIC FLOW

Journal of Mechanics in Medicine and Biology ◽

10.1142/s0219519416500111 ◽

2016 ◽

Vol 16 (02) ◽

pp. 1650011 ◽

Cited By ~ 3

Author(s):

ALI CEMAL BENIM ◽

FETHI GÜL ◽

ALEXANDER ASSMANN ◽

PAYAM AKHYARI ◽

ARTUR LICHTENBERG ◽

...

Keyword(s):

Boundary Condition ◽

Boundary Conditions ◽

Constant Pressure ◽

Loss Coefficient ◽

Human Aorta ◽

Retrograde Perfusion ◽

Heart Lung Machine ◽

Perfusion Mode ◽

Good Agreement ◽

Outlet Boundary Condition

Flow in a polyurethane model of a human aorta, driven by a heart-lung machine, is analyzed experimentally and computationally for antegrade and retrograde perfusion. The purpose of the analysis is the validation of the previously proposed loss-coefficient-based outlet boundary condition for aortic branches. This model is claimed to be commonly applicable to different perfusion modes of the aorta, unlike the alternative straightforward constant-pressure outlet boundary condition. First, the antegrade perfusion is analyzed computationally and experimentally. This step delivers the loss-coefficients that are to be used in any other perfusion mode of the aorta. Subsequently, a retrograde perfusion is applied to the same aorta, where the flow rates at the outlets of the aortic branches are measured and predicted by applying the loss-coefficient-based outlet boundary conditions. A very good agreement of the predictions with the measurements is observed. The predictions delivered by the standard constant-pressure outlet boundary condition are observed, on the contrary, to be highly in error. Thus, the advocated loss-coefficient-based outlet boundary condition is experimentally validated. It is shown that it is applicable to different perfusion modes with a quite good accuracy, which is much higher compared to the straightforward constant-pressure outlet boundary condition.

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NUMERICAL SIMULATION OF FREE VORTEX WITH MODIFIED NAVIER–STOKES CHARACTERISTIC BOUNDARY CONDITIONS

Modern Physics Letters B ◽

10.1142/s0217984910023554 ◽

2010 ◽

Vol 24 (13) ◽

pp. 1333-1336

Author(s):

LIN CHEN ◽

DENGBIN TANG ◽

XIN GUO

Keyword(s):

Boundary Condition ◽

Compressible Flows ◽

Diffusion Processes ◽

Stokes Equations ◽

Navier Stokes ◽

Free Vortex ◽

Navier Stokes Equations ◽

Characteristic Boundary ◽

Accurate Treatment ◽

Characteristic Boundary Condition

The convection and diffusion processes of free vortex in compressible flows are simulated by using high precision numerical method to solve for the Navier–Stokes equations. Accurate treatment of the boundary condition is extremely important for simulation of vortex flows. The developed numerical methods are well presented by combining six-order non-dissipation compact schemes with Navier–Stokes characteristic boundary condition having transverse and viscous terms, and can accurately simulate the movement of free vortex. The numerical reflecting waves at the boundaries are well controlled.

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